(1) Field of the Invention
The present invention relates to a fixing device and an image forming apparatus using the device, in particular relating to a fixing device using a fixing belt, for use in an image forming apparatus for forming images using toner based on electrophotography, such as an electrostatic copier, laser printer, facsimile machine or the like, as well as to an image forming apparatus using this device.
(2) Description of the Prior Art
Conventionally, an image forming apparatus based on electrophotography (for example, a printer) includes a fixing device which fuses a toner image formed on a recording sheet (recording paper or sheet) to fix the image onto the sheet. As an example of the fixing device, a paired roller type fixing device that is composed of a fixing roller and a pressing roller has been known.
The fixing roller is a roller component which is formed of a hollow metal core made of aluminum or the like and an elastic layer formed thereon and has halogen lamps as a heat source arranged inside the core.
In this arrangement, a temperature controller is also provided so as to control the surface temperature of the fixing roller by performing on/off control of the halogen lamps based on the signal output from a temperature sensor disposed on the fixing roller surface.
The pressing roller is a roller component composed of a metal core on which a heat-resistant elastic layer of silicone rubber or the like is formed as a coating layer. This pressing roller is put in pressure contact with the peripheral side of the fixing roller, forming a nip area between the fixing roller and the pressing roller due to the elastic deformation of the elastic layer of the pressing roller.
In the above arrangement of the fixing device, the paper with an unfixed toner image formed thereon is delivered into and between the fixing roller and the pressing roller or a nip area, and conveyed by these rollers as they rotate so that the toner image on the paper is heated by the peripheral side of the fixing roller and fused and fixed to the paper.
However, since the fixing and pressing rollers of the conventional paired roller type remain at room temperature when the image forming apparatus is turned on at the time of the first activation in the morning, the surface temperature of the rollers needs to be raised to a predetermined temperature after power activation, which requires warm-up time. Since it is also necessary to keep the roller surface at the predetermined temperature when the apparatus is in its standby mode in which no copying operation is performed, the fixing device needs to be heated constantly even when no copying operation is performed. In this way, the conventional configurations have the problem that waste energy is consumed by other than an image forming operation.
In order to solve the above problem, there is a proposal of a fixing device which does not use the fixing roller but uses a fixing belt having a lower heat capacity, instead (see Patent Document 1).
This fixing device includes a fixing roller and a curved plate-shaped heater and is constructed to heat and press the unfixed image formed on the recording medium by means of an endless fixing belt wound on the fixing roller and the outer peripheral side of the curved plate-shaped heater and a pressing roller.